In the process of manufacturing semiconductor devices, LCD panels, and others, there are hundreds of processing equipments and thus hundreds of manufacturing steps. Robot can be used to transport workpieces, typically stored in carrier boxes, from one location to another location, from one equipment to another equipment. In a process system, a robot is typically used to remove the workpieces from the carrier boxes, and then loaded into a loadlock. Another robot can be used to move the workpiece from the loadlock into a processing chamber, and from one processing chamber to another processing chamber. The processing system could be a stocker system, a sorter system, an ID reader system, a deposition system, an etch system, a lithography system, a metrology system, an inspection system, an implantation system, a treatment system, or any workpiece processing system.
It is very important to keep track of the flow of the wafers, flat panels, LCDs or reticles (hereafter workpiece) throughout the different processing steps, and to locate a particular workpiece at any given time. Further, it is desirable to be able to identify the workpiece to verify the appropriate processing steps designed for that workpiece. Thus typically each workpiece carries an identification (ID) mark before entering the fabrication facility. The mark can be read at an ID reader station, or at any processing station equipped with a reader. For semiconductor wafer, the mark is typically a bar code or a sequence of characters etched or scribed at an upper or lower surface near the outer circumference. The marked locations are typically at a standard location on one of its principal surfaces, usually adjacent a flat or notch on the periphery of the wafer so that the location of the mark can be determined through the orientation of the wafer.
The workpieces are generally processed with their top surface facing upward, but in some applications, workpieces are processed in both top up and top down orientations. Further, while the ID marks are typically on the top surface, some are located on the bottom surface. Thus, for high throughput workpiece identification, both sides of the workpiece would need to be read simultaneously. To read both sides of the substrate simultaneously using conventional systems typically requires two cameras and illumination systems with serious drawback for the utilization of a second system, such as space requirement, obstruction issue, equipment modification, and associated cost.